710 



SCIENCE. 



[N. S. Vol. XVI. No. 409. 



so-called false hybrids, in which in the second 

 generation the hybrid splits up into the parent 

 forms only. It is easily seen from what fol- 

 lows that this will necessarily be the case 

 when two plants are crossed each of which 

 responds to its own pollen more readily than 

 to that of the other. Cases like this are not 

 infrequent. [Referring to the above diagram, 

 we get the hybrid Ab in the first generation 

 by offering to ovules of B pollen of A only. 

 But when the hybrid produces pollen and 

 ovules, both A and B ovules are supplied with 

 both kinds of pollen; hence we get no hybrids 

 in the fertilization of the ovules on the hy- 

 brid. That is, A X A and B X B give fertile 

 seed and A X B and B X A fail because their 

 ovules are supplied with both kinds of pollen 

 and each responds more readily to its own than 

 to that of the other. Instead, therefore, of 

 being an exception to Mendel's law, Millar- 

 det's false hybrids fully conform to that law 

 and are explained by it. Correns' proposed 

 explanation of this case (See Ber. Deuisch. 

 Bot. Gcsel., April 24, 1901) as a limiting case 

 of a series, which is itself not satisfactorily 

 accounted for, cannot be accepted. 



Another case: sometimes a hybrid, instead 

 of showing progeny made up of plants, one 

 fourth of which are like the male parent, one 

 fourth like the female parent, and one half 

 like the hybrid, as is the case under Mendel's 

 law, seems at once to be fixed in type, and pro- 

 duces progeny of its own type only. From 

 what follows it will be seen that this is neces- 

 sarily the case, if Mendel's law is true, when 

 the two plants are each self-sterile or when 

 each responds to the pollen of the other more 

 readily than to its own, which is not infre- 

 quently the case. Referring again to the above 

 diagram illustrating Mendel's law : A X A 

 fails in this case because A ovules are offered 

 both A and B pollen and they fertilize only 

 with B pollen. Similarly, B ovules are offered 

 both A and B pollen and they fertilize only 

 with A pollen. We get therefore the fertiliza- 

 tions A X B and B X A, both of which pro- 

 duce only the hybrid. Again we see that Men- 

 del's law offers a perfectly rational explanation 

 of what has been stated as an important ex- 



ception to it. In this case I would suggest to 

 those who are in a position to do so that the 

 above explanations, which I present only as 

 hypotheses as yet, may be easily put to test, 

 by taking those cases in which these excep- 

 tional hybrids occur and ascertaining whether 

 or not the hypotheses here proposed accord 

 with the facts regarding the relative sterility 

 of the plants towards their own pollen and 

 that of the other party to the cross. 



Many other apparently abnormal cases are 

 to be explained on similar grounds; for in- 

 stance, if one plant is seK sterile or responds 

 more readily to pollen of the other plant than 

 to its own, while the other responds with equal 

 readiness to both kinds of pollen, we would 

 have a case like the following (see diagram) : 

 A X -^ would not occur, because A being of- 

 fered pollen of both A and B, all the A ovules 

 fertilize with B pollen. AXB and BXB 

 will occur as in the diagram. BXB will 

 constitute one fourth the progeny, while three 

 fourths will consist of the hybrid Ab; such 

 apparent anomalies are therefore entirely con- 

 sistent with Mendel's law. 



Some time in the near future I shall pre- 

 sent another case which seems to be a real 

 exception to this law (Correns' series above 

 referred to) and shall offer an explanation for 

 it and the results of experimental data. 



W. J. Spillman. 



Bureau of Plant Industry, 

 U. S. Dept. Ageic. 



A REALISTIC DEEAM. 



The following statement concerning a re- 

 markably realistic dream was written in the 

 form of a personal letter by Dr. Charles A. 

 White to his friend Mr. Arnold Burges John- 

 son, of Washington, D. 0. 



A VISION. 



My Dear Friend: 



In compliance with your request I herewith 

 send you an account of the visional dream to 

 which I referred in our conversation a few 

 days ago, together with some remarks upon it 

 and upon certain circumstances connected 

 with its occurrence. 



